Film Strength

[GMorg]

I see blenders making claims about film strength - film of next grade up or 4X stronger than competitor. It seems as though most measures would be confounded with additives for boundary lubrication and would not have anything to do with an actual oil film.

Is there an industry standard for measuring film strength? Can these claims be made with an objective measure?

 

[Darwin1138]

HTHS?

 

[GMorg]

Oils that claim 4X film strength do not have 4X HTHS.

 

[Kuato]

Originally Posted By: GMorg
Oils that claim 4X film strength do not have 4X HTHS.


Non linear relationship?

 

[tudorart]

Film strength includes solid films EP and boundary additives all coming from the oil. Misunderstanding is on your side.

Regarding HTHS...it's obvious viscosity helps film strength more so if you're looking for high shear behavior but it's not the whole story. It is however a standardized test that we can easily access for comparisons. It's been made to mimic bearing viscosity but correlates well with film thickness.

Other factors would be pressure-viscosity coefficient (behavior under elastodynamic film), unctuosity/polarity towards some materials but also types of surfaces,surface tension characteristic.
Some polymers or other additives may also give the film elasticity.

Yes there are certain machines used to measure strength but it really vary on application, pressures (with different direction and magnitude) etc

 

[GMorg]

I can always accept that I may be misunderstanding things. However, it seems that without extensive caveats (temperature, pressure, application, engine location, etc.), any claims about film strength are meaningless fluff.

If a company claims that their oil has 4X the film strength of another oil (and such claims are made in the US market), exactly what was measured and under what conditions. Without specifics, I think that such claims are deceptive at minimum.

My question remains. Are there industry standards for measurement of film strength? What are the units of this measurement? What controls must be enforced to make the measurement useful?

 

[Skid]

This thread from 10 years ago might answer your question.

http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4339/film_strength...

 

[GMorg]

Thanks for the link, Skid. Those were the days when BITOG particpants sought discussion over competition.

From that thread, it seems that each type of measurement protocol would be confounded by additives for boundary lubrication. However, the part of the discussion that related to longer molecules dragging more oil into the wedge can explain two apparent differences in film strength with two oils that were similar in viscosity. If two oils behave differently due to local pressures, temperature, and laminar shear, then one would appear to have a higher film strength...or at least it seems that way to me.

By the way, does anyone know of words that differentiate 1)the shear that relates to flow at rate higher than viscosity would predict from 2)the breakage of covalent bonds (like a permanently sheared polymer)?

 

[MolaKule]

One can test the film strength of base oils 'indirectly' by using the Load-to-Siezure test:

http://www.bobistheoilguy.com/forums/ubb...Oil#Post3435783

I am sure that someone somewhere has written a paper on the molecular bonding forces necessary to rip an oil molecule.

And the PI package could certainly affect the overall film strengths in the various regimes of the Stribeck curve.